US2593108A - Leather finishing - Google Patents

Description

Patented Apr. 15, 1952 LEATHER FINISHING Arthur Frederick Richmond Cotton, Merrick, N. Y.

No Drawing. Application July 3, 1947, Serial No.

758,992. In Great Britain March 18, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires March 18, 1960 3 Claims. (01. 69-21) This invention relates to the finishing of leather, that is to say to the processing of leather subsequent to tanning.

The invention provides a process for the finishing of leather, that is treatment subsequent to tanning, which consists in contracting the fibres of the leather by applying heat at a temperature of 240F. to 600 F. to one side or in succession to each side of the tanned skinor hide by means of a heat transmitting surface against which the leather is pressed by a presser member which is arranged to exert on the leather a pressure up to lbs. per square inch and which, as to that portion in contact with the leather, is of a porous and soft or resilient nature. A presser member of this kind facilitates the absorption of moisture and vapour formed during the heating process. By means of the aforesaid process according to the invention, the firmness and/or substance of the leather is improved and a much finer and closer grain is produced.

Incarrying out the present invention it is preferable to employ chrome tanned or semichrome tanned leathers, because they are capable of withstanding extremely high temperatures. Other mineral tannages may, however, be employed and vegetable tanned skins which have been semi-chromed by the known method of partially stripping the vegetable tannage and subsequently treating the skins in a crome bath mayalso be used. In some cases skins which have been subjected to the so-called synthetic tannages may also be used, but in such cases it may be necessary to treat the skins, e. g. by impregnation with a mineral compound, in order to render them suitable for withstanding the abnormal heat applied in carrying out the invention. .In this connection it is to be noted that if heat is applied. to' a vegetable tanned skin, the leather will begin todeteriorate at about 160 F. and may be destroyed at about 180-190. F. If, however, the leather is re-tanned with chrome or mineral solution itthen becomes capable of withstanding temperatures within the range of the plate itself.

2 grease in the leather whereby they are boile closely affects the contraction of the fibres.

An important application of the invention is to the improvement of thin inferior leathers. By applying the method of the invention to such leathers a very defective scarred skin which is too coarse for ordinary purposes may be sub stantially improved in grain and to some extent in substance and a finished leather obtained in which the natural defects are considerably obsoured.

In one example according to the invention the abnormal heat i applied to the leather surface to be treated by means of a stationary hot plate 7 which is maintained at the required temperature by any convenient heating means which may be thermostatically controlled. The surface of the leather to be treated is pressed against the hot plate by means of a cooperating presser plate which may be pneumatically controlled. One or more layers of absorbent material are interposed between the presser plate and the back of the leather, in order to provide a soft bed and to ensure that the steam and moisture formed during heating may be readily absorbed. In addition a suction fan or the like may be employed for removing excess moisture and vapour. It will be appreciated that by limiting the pressure exerted by the presser member to one not exceeding 10 lbs. per square inch, the leather is allowed to contract as a result of the application of heat while at the same time the necessary contact between the hot plate and the surface undergoing treatment is obtained to ensure the eifective transfer of heat.

The time during which the leather surface has been maintained in contact with the hot'plate depends to some extent on the degree of contraction required and in general it will vary in.- versely with variations in the temperature of the For most purposes satisfactory results are obtained by an application of heat for a .duration of 3-10 seconds. The application may be repeated several times to obtain the desired improvement in the leather.

The principal application of the invention is to the treatment of the grain side of the tanned skin in order to fine the grain, tighten the fibers or improve the substance of the leather. Before or after the grain side has been contracted it may, however, be desirable to process the flesh side of the leather in a similar way in order to dry out or contract the loose flesh fibers. The degree of contraction of the fibers is controllable bythe temperature employed, the duration of the heating, the moisture content of the leather, the substance of the leather and the extent to which the fat liquoring has been carried. In one example a skin which had been full chromed and fat-liquored by the usual methods was treated in an apparatus of the type described employing a hot plate and cooperating presser plate, by first applying heat to the flesh side of the skin (i. e. with that side next to the hot plate) at a temperature of about 330 F. and pressure of 4-6 lbs. per square inch for a period of about 3 seconds and thereafter applying heat at substantially the same temperature and pressure to the grain side of the skin for a period of about 20 seconds. The grain and substance of the leather were considerably improved.

The invention may be employed in conjunction with well known finishing operations such as dyeing, glazing, plating, graining, boarding and the like, the heating of the leather according to the invention being effected either at an intermediate stage in the usual operations or subsequent thereto.

Commercially available equipment for carrying out the present invention, customarily provides horizontal heated and presser plates with the heated plate above the presser plate: It may have to be altered respecting its heating system, to provide the high temperatures required by the present invention, but it is considered preferable that the normal plate arrangement should be maintained. It has already been explained that the presser plate must carry layers of absorbent material not only to provide a soft bed for the leather, but also to ensure that the steam and moisture formed during heating may be readily absorbed. This purpose may be interfered with if an attempt is made to process the leather with the latter in a vertical position, the steam rising, in such instances, and preventing uniform or controllable contraction of the leather. There may be instances when it is more convenient to use an angle from the horizontal in positioning the leather for treatment, but the closer this approaches the vertical the more chance there is for vapors to rise and perhaps cause uneven results when the invention is practiced.

Furthermore, it has been explained that the temperatures. producing the described results, depend on the degree of moisture in the leather, and that dryleather will withstand higher temperatures than leather in a moist condition. Due to the moisture absorbing characteristics of leather. it is practically impossible to treat leather that is completely free from moisture. The term dry is used in the sense that the leather should feel dry to the touch, it being possible. for a skilled leather worker to determine the relative degree. of dryness of leather by feeling it with his fingers. Even with leather well dried in a drying room with heat, the degree of dryness depends on the weather, and in England the relative average humidity is high, thus making the temperatures specified hereinbefore appropriate for that country.

In the United States the relative average humidity is lower. It follows that anyone practicing this invention in the United States automatically finds that the higher temperatures specified hereinbefore are more applicable, and that it is possible to go higher than 600 F. particularly if the leather is thoroughly impregnated with fat-liquor. A more appropriate temperature range for treating the leather in the United States has been found to be from about 300 F. to 700 F., or perhaps even higher by shortening the contact time between the hot plate and leather.

Once it is understood that comparatively dry leather can be contractedin the manner described, it is possible to determine the appropriate temperature to be used for any particular batch of leather. This also applies to the contact time between the hot plate and leather. As previously indicated the hot plate should be hot enough to appreciably contract the leather with a contact time of about 3 seconds, with the application repeated as required to obtain the desired improvement in the leather, the upper temperature limits being determinable by the tolerable contact time becoming too short for convenience.

When the treatment is applied to both sides of the leather as has been described, a new article of manufacture is obtained that was previously unknown to the leather industry. This product comprises a piece of leather that is mineral tanned, in the sense that its tanning included at least some mineral tannage, with the fibers of both sides of the leather contracted and firmed where they were afiected by the heat. Visual observation of a cross section of the treated leather shows that the fibers are contracted as described, a cross section of the leather having the appearance of having two grain sides insofar as the fiber interlacing is concerned. Such leather has a higher tensile strength than other leather of the same kind. This new product results from practicing the method.

The term mineral tannage is used herein in the sense of meaning a material withwhich the skin or leather may be tanned or impregnated to increase its resistance to the heat required by the present invention. Tannages are now in a state of development and it is possible that tannages, other than thus classified, may be produced which will permit the skin or leather to withstand the high heating disclosed herein. It is intended that such tannages be considered the equivalent of a mineral tannage. Also, the term skin as used herein is intended to embrace light and heavy hides, as well as skins, it being used for convenience to designate the raw material prior to tanning.

I claim:

1. A leather finishing process including applying heat to at least one side of leather, with the heat hot enough to materially contract the leather and with the leather permitted to contract and with the leather contacted by a moistureabsorbent bed.

2. A leather finishing process including applying heat to at least one side of leather, with the heat hot enough to materially contract the leather and with the leather permitted to contract and with one side of the leather contacted by a moisture-absorbent bed, with the heat applied by a heated plate contacted with the other side of the leather and limited to a short time interval repeated if required to obtain greater contraction, and with the heat successively applied to opposite sides of the leather.

3. A leather finishing process including contacting leather by a moisture-absorbent bed, and contacting the other side of the leather with a plate heated to a temperature in excess of 240 F., with a contact pressure not exceeding about 10 pounds per square inch and for atime not exceeding 10 seconds constant duration, the leather being enough tanned with a tannage causing the leather to withstand the heat of the plate and containing grease, and the maximum temperature of the plate being less than that which deteriorates the leather with the minimum practical contact of the plate with the leather, the minimum temperature of the plate being sufllcient to e1; ct noticeable contraction of the leather being I ocessed.

FREDERICK RICHMOND CO'ITON. m

6 REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,115,182 Enslin Oct. 27, 1914 1,115,183 Enslin Oct. 27, 1914 2,272,935 Cotton Feb. 10, 1942